Reusable code that treats TWiki forms data as if it were a database

---+ Summary of Contents

This module supports structured queries over a database built on the fly from the forms in TWiki topics. It does not support any tags, as it is provided as a service for other plugins that want to treat a TWiki web as a simple database; for example, the TWiki:Plugins/FormQueryPlugin, which supports the display of query results.

The plugin encapsulates code that was formerly in the "engine room" of the FormQueryPlugin. It has been abstracted out in the belief that it will be useful to anyone who wants to do simple search operations from a plugin.

---++ Features
	* Perform complex queries on the TWiki database
	* Cache TWiki topics for rapid queries

---++ How the database gets built
You can think of the database as an array of all the topics in a web. Each array entry is a map (or hash in perl terms) that maps a set of field names to values.

Each topic in the web automatically gets a number of standard fields, generated by reading the metadata from the topic (see %TWIKIWEB%.TWikiMetaData)
	* =name=		  - name of the topic
	* =parent=		- name of parent topic
	* =_up=			- _reference_ to the Map of the parent topic, if it exists
	* =attachments= - array of Maps, each of which contains:
		*  =_up= - _reference_ to the Map for the topic
		*  =name= - attachment name
		* =attr= - e.g hidden
		* =comment= - attachment comment
		* =path= - client path used to upload attachment
		* =size= - size in Kb
		* =user= - who uploaded the attachment
		* =version= - e.g. 1.3
	* =info= - Map containing:
		* =_up= - reference to the Map for the topic
		* =author= - most recent author
		* =date= - date of last change
		* =format= - topic format version
		* =version= - topic version number
	* =moved= - Map containing:
		* =_up= - reference to the Map for the topic
		* =by= - who moved it
		* =date= - when they moved it
		* =from= - where they moved it from
		* =to= - where they moved it to
	* =form= - form type
	*  _form name_ - e.g. if a "My<nop>Form" is attached, this will be =My<nop>Form=. This is a reference to a Map containing a key for each field in the form. Each key maps to the value in the form data for that key. The Map will also have an =_up= reference to the Map for the topic.
	* =text= - raw text of the topic)

The sub-Maps created for =info=, _form name_, =moved=, and each row in =attachments= also have a _reference_ back to the topic Map, called  =_up=.

Other fields may be added by subclasses. Refer to the documentation for the plugin that is using the DBCache for more details.

---++ The cache
To achieve best perfomance the plugin caches the database read from the TWiki topics. It creates this cache in a file in the web, <code>_DB<nop>Cache</code>. If any topic changes in the web, this cache is automatically rebuilt. The cache file can be deleted at any point with no ill effects.
---++ Extending or customising
Extension or customisation is welcome, as long as all extensions are described and code provided back to the author.

The module is shipped with a perl build file, which should be used for installation and testing. Testing is done using CPAN:Test::Unit, and is invoked using the 'test' build target. Writing tests is a useful way of feeding back bugs as well. I can't encourage you enough to maintain and extend the tests!
---+ Detailed Documentation
Clients use the DBCache by defining a subclass of the =TWiki::Contrib::DBCache= class. The following POD documentation describes the methods of this class and the various other classes provided by the plugin..

---++ class DBCacheContrib

General purpose cache that treats TWiki topics as hashes. Useful for
rapid read and search of the database. Only works on one web.

Typical usage:
<verbatim>
  use TWiki::Contrib::DBCacheContrib;

  $db = new TWiki::Contrib::DBCacheContrib( $web ); # always done
  $db->load(); # may be always done, or only on demand when a tag is parsed that needs it

  # the DB is a hash of topics keyed on their name
  foreach my $topic ($db->getKeys()) {
	  my $attachments = $db->get($topic)->get("attachments");
	  # attachments is an array
	  foreach my $val ($attachments->getValues()) {
		 my $aname = $attachments->get("name");
		 my $acomment = $attachments->get("comment");
		 my $adate = $attachments->get("date");
		 ...
	  }
  }
</verbatim>
As topics are loaded, the readTopicLine method gives subclasses an opportunity to apply special processing to indivual lines, for example to extract special syntax such as %ACTION lines, or embedded tables in the text. See FormQueryPlugin for an example of this.


---+++ =new($dataDir, $web)=
	* =$dataDir= location of cache file
	* =$web= name of web to create the object for.
Construct a new DBCache object.


---+++ readTopicLine($topic, $meta, $line, $fh) --> text
	* $topic - name of the topic being read
	* $meta - reference to the hash object for this topic
	* line - the line being read
	* $fh - the file handle of the file
	* __return__ text to insert in place of _line_ in the text field of the topic
Called when reading a topic that is being cached, this method is invoked on each line
in the topic. It is designed to be overridden by subclasses; the default implementation
does nothing. The sort of expected activities will be (for example) reading tables and
adding them to the hash for the topic.


---+++ onReload($topics)
	* =$topics= - perl array of topic names that have just been loaded (or reloaded)
Designed to be overridden by subclasses. Called when one or more topics had to be
read from disc rather than from the cache. Passed a list of topic names that have been read.


---+++ load()

Load the web into the database.
Returns a string containing 3 numbers that give the number of topics
read from the cache, the number read from file, and the number of previously
cached topics that have been removed.


---+++ write($archive)
	* =$archive= - the TWiki::Contrib::DBCacheContrib::Archive being written to
Writes this object to the archive. Archives are used only if Storable is not available. This
method must be overridden by subclasses is serialisation of their data fields is required.


---+++ read($archive)
	* =$archive= - the TWiki::Contrib::DBCacheContrib::Archive being read from
Reads this object from the archive. Archives are used only if Storable is not available. This
method must be overridden by subclasses is serialisation of their data fields is required.


---++ class Search
Search operators work on the fields of a TWiki::Contrib::DBCacheContrib::Map. The fields are given by name, and the values by strings. Strings should always be surrounded by 'single-quotes'. String which are regular expressions use 'perl' re syntax (see =man perlre= for help)

*Warning* single and double quotes are not allowed in values!

The following operators are available:

| *Operator* | *LHS* | *RHS* | *Meaning* |
| <code>=</code> | field name | regular expression | Value exactly matches this regular expression. The expression must match the whole string. |
| <code>!=</code> | field name | regular expression | Field is not this RE. Inverse of = |
| <code>=~</code> | field name | regular expression | Value contains this regular expression i.e. the RE is found somewhere in the field value. |
| <code>&lt;</code> | field name | integer (string containing an integer e.g '4') | Number is < |
| <code>&gt;</code> | field name | integer | Number is > |
| <code>&gt;=</code> | field name | integer | Number is >= |
| <code>&lt;=</code> | field name | integer | Number is <= |
| <code>EARLIER_THAN</code> | field name | date (string containing a date e.g. '1 Apr 2003' | Date is earlier than the given date |
| <code>LATER_THAN</code> | field name | date | Date is later than the given date |
| <code>WITHIN_DAYS</code> | field name | integer | Date (which must be in the future) is within n _working_ days of todays date |
| <code>!</code> | none | expr | Boolean NOT |
| <code>AND</code> | expr | expr | Boolean AND |
| <code>OR</code> | expr | expr | Boolean OR |
| <code>()</code> | N/A | N/A | Bracketed subexpression |

Dates for =EARLIER_THAN=, =LATER_THAN= and =WITHIN_DAYS= must be dates in the format expected by =Time::ParseDate= (like the ActionTrackerPlugin). =WITHIN_DAYS= works out the number of _working_ days (i.e. excluding Saturday and Sunday). Apologies in advance if your weekend is offset &plusmn; a day!

A search object implements the "matches" method as its general
contract with the rest of the world.

---+++ Example
Get a list of attachments that have a date earlier than 1st January 2000
<verbatim>
  $db = new TWiki::Contrib::DBCacheContrib::DBCache( $web ); # always done
  $db->load();
  my $search = new TWiki::Contrib::DBCacheContrib::Search("date EARLIER_THAN '1st January 2000'");

  foreach my $topic ($db->getKeys()) {
	  my $attachments = $topic->get("attachments");
	  foreach my $val ($attachments->getValues()) {
		 if ($search->matches($val)) {
			 print $val->get("name") . "\n";
		 }
	  }
  }
</verbatim>


---+++ =new($string)=
	* =$string= - string containing an expression to parse
Construct a new search node by parsing the passed expression.


---+++ =matches($object)= -> boolean
	* =$object= - object to test; must implement =get=
See if object matches the search. =$object= can actually be any object that provides
the method "get" that returns a value given a string key.


---+++ =toString()= -> string
Generates a string representation of the object.


---++ class FileTime

Object that handles a file/time tuple for use in Storable and
=TWiki::Contrib::DBCacheContrib::Archive=.


---+++ =new($file)=
	* =$file= - filename
Construct from a file name


---+++ =uptodate()= -< boolean
Check the file time against what is seen on disc. Return 1 if consistent, 0 if inconsistent.


---+++ =toString()= -> string
Generates a string representation of the object.


---+++ =write()=
TWiki::Contrib::DBCacheContrib::Archive hook


---+++ =read()=
TWiki::Contrib::DBCacheContrib::Archive hook


---++ class Array

Generic array object. This is required because perl arrays are not objects, and
cannot be subclassed e.g. for serialisation. To avoid lots of horrid code to handle
special cases of the different perl data structures, we use this array object instead.


---+++ =new()=
Create a new, empty array object


---+++ =add($object)=
	* =$object= any perl data type
Add an element to the end of the array


---+++ =find($object)= -> integer
	* $object datum of the same type as the content of the array
Uses "==" to find the given element in the array and return it's index


---+++ =remove($index)=
	* =$index= - integer index
Remove an entry at an index from the array.


---+++ =get($key, $root)= -> datum
	* =$k= - key
	* $root - what # refers to
*Subfield syntax*
	* =get("9", $r)= where $n is a number will get the 9th entry in the array
	* =get("[9]", $r)= will also get the 9th entry
	* =get(".9", $r)= will also get the 9th entry
	* =get(".X", $r)= will return the sum of the subfield =X= of each entry
	* =get("[?<i>search</i>]", $r)= will perform the given search over the entries in the array. Always returns an array result, even when there is only one result. For example: <code>[?name='Sam']</code> will return an array of all the entries that have their subfield =name= set to =Sam=.
	* =#= means "reset to root". So =get("#[3]", $r)= will return the 4th entry of $r (assuming $r is an array!).
	* =get("[*X]", $r)= will get a new array made from subfield X of each entry in this array.

Where the result of a subfield expansion is another object (a Map or an Array) then further subfield expansions can be used. For example,
<verbatim>
get("parent.UserTable[?SubTopic='ThisTopic'].UserName", $web);
</verbatim>

See also =TWiki::Contrib::DBCacheContrib::Map= for syntax that applies to maps.


---+++ =size()= -> integer
Get the size of the array


---+++ =sum($field)= -> number
	* =$field= - name of a field in the class of objects stored by this array
Returns the sum of values of the given field in the objects stored in this array.


---+++ =search($search)= -> search result
	* =$search= - TWiki::Contrib::DBCacheContrib::Search object to use in the search
Search the array for matches with the given object.
values. Return a =TWiki::Contrib::DBCacheContrib::Array= of matching entries.


---+++ =getValues()= -> perl array

Get a "perl" array of the values in the array, suitable for use with =foreach=


---+++ =toString($limit, $level, $strung)= -> string
	* =$limit= - recursion limit for expansion of elements
	* =$level= - currentl recursion level
Generates an HTML string representation of the object.


---+++ write($archive)
	* =$archive= - the TWiki::Contrib::DBCacheContrib::Archive being written to
Writes this object to the archive. Archives are used only if Storable is not available. This
method must be overridden by subclasses is serialisation of their data fields is required.


---+++ read($archive)
	* =$archive= - the TWiki::Contrib::DBCacheContrib::Archive being read from
Reads this object from the archive. Archives are used only if Storable is not available. This
method must be overridden by subclasses is serialisation of their data fields is required.


---++ class Map
Generic map object for mapping names to things. A name is defined as
  =name = \w+ | \w+ "." name=
The . indicates a field reference in a sub-map.
Objects in the map are either strings, or other objects that must
support toString.


---+++ =new($string)=
	* $string - optional attribute string in standard TWiki syntax
Create a new, empty array object. Optionally parse a standard attribute
string containing name=value pairs. The
value may be a word or a quoted string (no escapes!)


---+++ =fastget($k)= -> datum
	* =$k= - key
Get the value for a key, but without any subfield field expansion


---+++ =get($k, $root)= -> datum
	* =$k= - key
	* =$root= what # refers to
Get the value corresponding to key =$k=; return undef if not set.

*Subfield syntax*
	* =get("X",$r)= will get the subfield named =X=.
	* =get("X.Y",$r)= will get the subfield =Y= of the subfield named =X=.
	* =get("[X]",$r) = will get the subfield named =X= (so X[Y] and X.Y are synonymous)..
	* =#= means "reset to root". So =get("#.Y", $r) will return the subfield =Y= of $r (assuming $r is a map!), as will =get("#[Y]"=.

Where the result of a subfield expansion is another object (a Map or an Array) then further subfield expansions can be used. For example,
<verbatim>
get("UserTable[0].Surname", $web);
</verbatim>

See also =TWiki::Contrib::DBCacheContrib::Array= for syntax that applies to arrays.


---+++ =set($k, $v)=
	* =$k= - key
	* =$v= - value
Set the given key, value pair in the map.


---+++ =size()= -> integer
Get the size of the map


---+++ =remove($index)= -> old value
	* =$index= - integer index
Remove an entry at an index from the array. Return the old value.


---+++ =getKeys()= -> perl array

Get a "perl" array of the keys in the map, suitable for use with =foreach=


---+++ =getValues()= -> perl array

Get a "perl" array of the values in the Map, suitable for use with =foreach=


---+++ =search($search)= -> search result
	* =$search= - TWiki::Contrib::DBCacheContrib::Search object to use in the search
Search the map for keys that match with the given object.
values. Return a =TWiki::Contrib::DBCacheContrib::Array= of matching keys.


---+++ =toString($limit, $level, $strung)= -> string
	* =$limit= - recursion limit for expansion of elements
	* =$level= - currentl recursion level
Generates an HTML string representation of the object.


---+++ write($archive)
	* =$archive= - the TWiki::Contrib::DBCacheContrib::Archive being written to
Writes this object to the archive. Archives are used only if Storable is not available. This
method must be overridden by subclasses is serialisation of their data fields is required.


---+++ read($archive)
	* =$archive= - the TWiki::Contrib::DBCacheContrib::Archive being read from
Reads this object from the archive. Archives are used only if Storable is not available. This
method must be overridden by subclasses is serialisation of their data fields is required.


---++ class Archive
Simple file archive storer and restorer. Handles serialising objects
using their "write" and "read" methods. Serialisable objects must
have a no-parameters constructor.

This module is only used if Storable isn't available. Storable is
much faster, because it is implemented in C.


---+++ =new($file, $rw)=
	* =$file= - archive file path
	* =$rw= - mode "r" or "w"
Create a new archive, using filename $file and
mode $rw which must be "r" or "w". The archive will remain
in existence (and the file remain open) until "close" is
called. An exclusive lock is taken for write as long as the file
is open. Throws an exception if the archive cannot be opened.


---+++ =close()=
Close this archive. MUST be called to
close the file.


---+++ =writeByte($b)=
	* =$b= - byte to write
Write a byte to the archive


---+++ =writeString($s)=
	* =$s= - string to write
Write a string to the archive


---+++ =writeInt($i)=
	* =$i= integer to write
Write a 32-bit integer to the archive


---+++ =writeObject()=
Write an object to the archive. An object must implement
=read($archive)= and =write($archive)=, or may be undef or a string. No other types
are supported.


---+++ =readByte()= -> byte
Read a byte from the archive


---+++ =readString()= -> string
Read a UTF8 string from the archive


---+++ =readInt()= -> integer
Read a 32-bit integer from the archive


---+++ =readObject()= -> object
Read an object from the archive


#SettingsAnchor
---+ Settings
	* Name of the perl package
		* Set STUB = TWiki::Contrib::DBCacheContrib
---+ Installation Instructions
	* Download the ZIP file from the Plugin web (see below). Contents:
	| *File:* | *Description:* |
	| ==lib/TWiki/Contrib/DBCacheContrib.pm== | Web cache class |
	| ==lib/TWiki/Contrib/DBCacheContrib/Search.pm== | SQL-style syntax search object |
	| ==lib/TWiki/Contrib/DBCacheContrib/FileTime.pm== | Cache support for remembering file dates |
	| ==lib/TWiki/Contrib/DBCacheContrib/Array.pm== | Array class  |
	| ==lib/TWiki/Contrib/DBCacheContrib/Map.pm== | Map class  |
	| ==lib/TWiki/Contrib/DBCacheContrib/Archive.pm== | Archiver used if Storable is not available  |
	| ==data/TWiki/DBCacheContrib.txt== | Documentation topic  |

	* Unzip ==%TOPIC%.zip== in your twiki installation directory.
	* Optionally, run ==%TOPIC%_installer== to automatically check and install other TWiki modules that this module depends on. You can also do this step manually.
	* Alternatively, manually make sure the dependencies listed in the table below are resolved.
	<table border="1"><tr><th>Name</th><th>Version</th><th>Description</th></tr><tr><td align="left">Time::ParseDate</td><td align="left">Required. Available from [[http://cpan.uwinnipeg.ca/dist/Time-modules][CPAN]].</td></tr><tr><td align="left">Storable</td><td align="left">Recommended; accelerates cache handling. Available from [[http://cpan.uwinnipeg.ca/dist/Storable][CPAN]]</td></tr></table>

---+ Contrib Info
|  Author: | TWiki:Main/CrawfordCurrie |
|  Copyright &copy;: | This code is based on an original development of Motorola Inc. and is protected by the following copyrights: <br>Copyright @copy 2002-2003 Motorola Inc. All Rights Reserved. <br>Portions copyright &copy; 2004. Crawford Currie http://www.c-dot.co.uk |
|  License: | As required for the publication of all extensions to TWiki, this software is published under the terms of the GNU General Public License. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details, published at http://www.gnu.org/copyleft/gpl.html |
|  Version: | 8670 |
|  Change History: | 8 Jul 2004: Initial version, split out from FormQueryPlugin |
|  Dependencies: | <table border="1"><tr><th>Name</th><th>Version</th><th>Description</th></tr><tr><td align="left">Time::ParseDate</td><td align="left">Required. Available from [[http://cpan.uwinnipeg.ca/dist/Time-modules][CPAN]].</td></tr><tr><td align="left">Storable</td><td align="left">Recommended; accelerates cache handling. Available from [[http://cpan.uwinnipeg.ca/dist/Storable][CPAN]]</td></tr></table> |
|  Perl Version: | 5.0 |
|  Plugin Home: | http://TWiki.org/cgi-bin/view/Plugins/%TOPIC% |
|  Feedback: | http://TWiki.org/cgi-bin/view/Plugins/%TOPIC%Dev |
|  Demo URL: | |

-- TWiki:Main/CrawfordCurrie - 16:41:47 01 February 2006
